Solids exist in either amorphous or crystalline forms. In the case of crystalline forms, molecules are positioned in three-dimensional lattice sites. When a compound recrystallizes from a solution or slurry, it may crystallize with different spatial lattice arrangements, and the different crystalline forms are sometimes referred to as “polymorphs.” The different crystalline forms of a given substance may differ from each other with respect to one or more chemical properties (e.g., dissolution rate, solubility), biological properties (e.g., bioavailability, pharmacokinetics), and/or physical properties (e.g., mechanical strength, compaction behavior, flow properties, particle size, shape, melting point, degree of hydration or solvation, caking tendency, compatibility with excipients). The variation in properties among different crystalline forms usually means that one crystalline form may be more useful compared to other forms. For example, Form A, Form D, and Form J of grapiprant are known to exhibit different physical properties from one another.
Because grapiprant exhibits several advantageous therapeutic properties, improved forms of the compound are desired, particularly with regard to enhanced solubility, bioavailability, ease of synthesis, ability to be readily formulated, and/or physical stability. Thus, there is a need for improved crystalline forms of grapiprant and methods for preparing the different forms.